1. Field of the Invention
The present invention relates to a thin film vacuum evaporation device, and more particularly, it relates to a thin film vacuum evaporation device in which a beam of light is directed to a target set in a vacuum to evaporate a part of the target, so as to make a film.
2. Description of the Background Art
There has been growing an interest in a method where a light source high luminous intensity, such as a laser beam, is employed as a means for forming a thin film of a substance having a high fusing point and high insulating property, such as ceramics. FIG. 1 is a schematic diagram showing a conventional thin film vacuum evaporation device.
As shown in FIG. 1, a discharging means 3 is connected to a reaction chamber 2 having a light transmitting window 1. This discharging means 3 functions to keep a hard vacuum in the reaction chamber 2 at the level of 10.sup.-3 Torr, desirably at the level of 10.sup.-4 to 10.sup.-6 Torr. In the reaction chamber 2, a target 4 consisting of alumina, quartz glass, or the like is rotatably held. Further, a member 5 to be deposited, such as a substrate, is disposed opposite to the target 4, and a heater 6 is placed for heating the substrate 5. Outside the reaction chamber 2, for example, a laser oscillator 7 such as a CO.sub.2 laser oscillator is placed. Laser beam 8 emitted from the laser oscillator 7 reflects at a mirror 9, focuses through the focusing lens 10, passes through the light transmitting window 1, and strikes against the target 4.
With this thin film vacuum evaporation device, first the reaction chamber 2 is brought to a hard vacuum through the discharging means 3. Then, the target 4 is rotated in a specified direction. While the substrate 5 is heated by the heater 6, as required, the laser beam 8 is emitted by the laser oscillator 7. The laser beam 8 emitted by the laser oscillator 7 reflects at the mirror 9, focuses through the focusing lens 10, passes through the light transmitting window 1 and strikes against the target 4. Thus, due to the laser beam 8 focusing on the target 4, the energy density of the laser beam 8 on the target 4 is very high. This enables the target 4 made of a substance having a high fusing point, such as alumina quartz glass, etc., to fuse and evaporate. The vapor produced from the target 4 is not scattered by the remaining gas in the reaction chamber 2, because a hard vacuum is kept in the reaction chamber 2, and most of the vapor reaches to the substrate 5. The vapor is deposited and solidified on the surface of the substrate 5 to be a thin film.
The thin film is formed in the way as has been described. However, a part of molecules composing the target 4 may be decomposed on evaporation, and hence, the composition of the thin film and that of the target 4 are not necessarily the same. For example, when oxide such as quartz glass and alumina is evaporated and deposited, a thin film having a slightly low oxygen concentration may often be formed. Usually, such a film does not fixedly adhere to the substrate 5 and easily comes off.
To improve the quality of the film, usually the vapor deposition is performed in an atmosphere of a reaction gas. If an oxide is used, the vapor deposition is performed in the atmosphere of oxygen. However, to improve the quality of the film in this way, the pressure within the reaction chamber 2 must be considerably high, and a large quantity of gas is required. Consequently, because of the scattering of the vapor against the reaction gas, there arises the problem that the speed of the vapor deposition is lowered, or the heater 6 for heating the substrate 5 is deteriorated due to oxidation. When an oil diffusing pump is used as the discharging means 3, the counter-flow rate of vaporized oil is increased. This causes the problem that the substrate 5 and the thin film are polluted by the oil, or the lifetime of the pump is shortened because of significant oxidation of the oil.
The vapor generated from the target 4 moves in all the directions, and then a small quantity of it reaches the light transmitting window 1 and adheres to the surface thereof. This gradually clouds the light transmitting window 1 to reduce the transmissivity. The transmissivity is lowered as much as 16% by simply performing the vapor deposition for 30 minutes after 100 W energy is supplied by the laser power source. As the transmissivity reduces, a part of the laser energy is absorbed by the light transmitting window 1, and hence the temperature of the light transmitting window 1 rises. The rising in temperature causes the change in the refractive index of the light transmitting window 1, and then this causes thermal lens effect. The thermal lens effect results in the energy density on the target 4 decreasing, and then this results in lowering the vaporizing speed. As a result, the light transmitting window 1 must be changed properly. With a conventional device, its light transmitting window must be changed every 20- to 30-minute-vapor deposition. Every time the light transmitting window 1 is changed, a vacuum state in the reaction chamber 2 is to be released, and this causes the disadvantage that the manufacturing efficiency is very poor.